Copper-tarnish inhibitor



United States I Patent" No Drawing. Filed Sept. 18, 1958, Ser. No. 761,668 1 Claim. (CI. 21-25) This invention relates to improvements in preventing the tarnishing and corrosion of copper and copper-alloy articles caused by the various compounds normally present n the air, namely, moisture, sulfur dioxide, oxygen, and m coastal areas, salt, that form stains, discolorations, filming on said articles, or a coating of basic copper sulfate, carbonate or oxychloride thereon.

This problem of corrosion, oxidizing and tarnishing is ever present in the fabrication, processing and storage of copper and copper-alloy articles, and the principal object of my invention is to so package said articles at any stage of their fabrication, that such deterioration of the metal is inhibited, effecting said result in a manner that is easy to carry out, is economical and which will not affect the finish of the metal.

Another object of the invention is to accomplish this inhibitory action by exposing the surface of the metal articles to the action of a protective medium that has the property of forming a barrier between the atmosphere and the surface to be protected.

Still another object of my invention is to provide such an inhibitor that does not have to be sprayed, brushed or otherwise coated on the metal, and hence there is no need of subsequently requiring removal of additive material from the metal being protected, before further use of the metal article may be had.

A further object of the invention is to inhibit corrosion of the aforesaid metals by exposing them to the presence of an amide of a fatty acid, so that under normal use, the amide is able to vaporize or sublime to set up a barrier that inhibits attack of the metal surface by elements normally present in the ambient atmosphere.

An added object of my invention is to incorporate said inhibitory substance with a suitable carrier, so that placement of the thus treated carrier in the near vicinity of the articles to be treated, will protect the latter against corrosion, the cheapest and probably the most convenient way of using said carrier being by wrapping or otherwise encasing the articles therein.

I have found that one of the fatty acid amides containing an NH; or CONH, radical at one of its ends, the amide being preferably a saturated one from the group exemplified by oleic acid, stearic acid, palmitic acid, and other generally high molecular weight fatty acid amides that have an alkyl chain length of up to 22 carbon atoms. and having the general formulation of or derivatives of the same, are admirably suited for use in the practice of my invention, as they will not deteriorate over long periods of time and may be held indefinitely, inasmuch as their thermal decomposition does not begin until above 175 C., and therefore such inhibitory materials are ideally suited for protecting the surfaces of such copper and copper alloy metals at any of their various stages of fabrication and through their storage periods.

Such fatty acid amides are substantially insoluble in water at normal room temperatures, but are soluble in ketones, esters, alcohols, turpentine, mineral spirits, fats and fatty acids, such solubility of course increasing proportionately with increased temperatures.

The aforesaid inhibitory substances are only slightly volatile, so that when incorporated with their carrier sheet and the metal articles then encased in the latter, they vaporize, volatilize or sublime slowly at ordinary room temperatures, the CONH radical at one end of the compound tending to attach itself to the metal, while the radical at the other end is water-repellant and acts as a barrier to prevent the transference of the metal-attacking substances between the atmosphere and said metal.

Best conditions for preventing such attack of the metal, and this is true for copper and copper alloys, is when the inhibitory substance has a pH of substantially between 6 to 8, said aforesaid amides falling within said range, and to further insure against tarnish it is preferred that the carrier sheet itself have substantially the same pH range.

In the carrying out of this invention, the selected fatty acid amide, or a mixture of the suitable ones, of relatively high molecular weight, is uniformly dispersed onto the carrier sheet. This may be done by liquifying the inhibitor alone, or with diluent oils, resinous sub stances, waxes, etc., combined therewith, or the inhibitor may be dissolved in a suitable preferably extremely fastevaporating solvent such as isopropyl alcohol, trichlorethylene, etc.

The amide thus prepared for use in treatment of the sheet may be impregnated on the latter, or may be coated one or both faces thereof, the degree of loading or concentration depending of the probable duration of exposure of the metal, conditions existing during such exposure, absorbency of the carrier material, etc., and from tests I have found that a solid concentration or load of from about .5 gram to 1 gram of the amide to each square foot of carrier is sufficient for most practical purposes and will adequately protect the metal metal against deterioration from the elements norm-ally found in the atmosphere.

The copper or copper alloy article or articles may be encased in said thus treated container or wrapper, and for best results I have found that the articles should be tightly or closely wrapped within the sheet.

When thus wrapped, the amides volatilize slowly to set up a barrier against transference to the articles of such atmospheric elements that would tend to have corrosive action on them.

Although the foregoing description was directed to the copper and copper alloy articles that were to be treated to prevent corro'sion, tests have shown that other non-fen rous metals are equally benefited by wrapping or encase ment in 2. treated sheet of the kind hereinbefore described, some of the metals having been so tested being zinc, tin, aluminum, chromium, nickel, etc., and in all of the articles having surfaces of said metals or alloys thereof or coatings, no tarnish or other corrosion developed after prolonged encasement.

4) References Cited in the file of this patent UNITED STATES PATENTS Hutter Dec. 12, 1950 Andersen Nov. 17, 1959 OTHER REFERENCES Volatile Rust Inhibitors, NRL Report 4319, March 10, 1954, Naval Research Laboratory, Washington, DC, p. 15. 

